This application claims an invention which was disclosed in Japanese application number 2002-146545, filed May 21, 2002, entitled xe2x80x9cMETHOD OF RECORDING AND READING INFORMATION USING MOLECULAR ROTATIONxe2x80x9d. The benefit under 35 USCxc2xa7119(a) of the Japanese application is hereby claimed, and the aforementioned application is hereby incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method of recording and reading information using the rotational phase of a molecule. More specifically, it relates to a method of implementing a memory that stores and reads information in a single molecule by using the tip of a scanning probe microscope to control the phase information for rotation within a molecule, and further using this tip to read the phase information.
2. Description of the Related Art
The scanning probe microscope (SPM) allows a single atomic molecule to be used for memory. However, in the methods that have been invented and proposed to date, position information is recorded by moving or removing atoms or molecules using the tip of a scanning probe microscope. In these methods, it is theoretically impossible to record numbers other than zeros and ones, that is to say, the digital information regarding the presence or absence of an atom or molecule. Furthermore, as the atoms or molecules were moved or removed each time that data was recorded or read, practical application thereof required a great deal of effort, and it was difficult to surpass the capacities of existing recording media.
Single molecule motors, such as the ATPase flagella motors existing in nature, are known. The rotation of these motors can be observed with an optical microscope. ATPase has also been used to make an artificial molecular motor. Furthermore, researchers have observed the rotation of molecules adsorbed on a metal surface by scanning probe microscope. However, the prior art has not used the rotational information of a molecular motor in a memory system.
Research using a femtosecond laser to control the phase information of molecules has been looked to as a form of quantum computing, and some attempts have been applied. However, the femtosecond lasers used in the prior art represent large-scale equipment. Quantum computing, as understood in the prior art, shows that, in accordance with decoherence theory, coherence will inevitably break down as system size increases, rendering impossible computations which require coherence to be maintained for long periods of time. This makes practical implementation extremely difficult.
The method of the present invention overcomes the disadvantages of the prior art. A particular object is to record phase information at the single molecule level. A further object is to record data in such a way as to exceed the density limits of digital recording, which are determined by the size of atomic molecules, and to exceed the recording densities assumed in the prior art.
More specifically, in the present invention, phase information is recorded at the single molecule level by controlling the phase information of the rotation within a single molecule with an electromagnetic field produced by the tip of a scanning probe microscope, and by using this tip as a probe so as to retrieve the rotational phase information of a single molecule. Consequently, it is possible to record data in such a way as to exceed the density limits of digital recording, which are determined by the size of atomic molecules, and to exceed the recording densities assumed in the prior art. In other words, as molecular rotation has a degree of freedom of 360xc2x0, large amounts of information can be stored in a single molecule, which is markedly different from digital recording elements comprising zeros or ones as known in the prior art.
In general, the phase information possessed by molecules takes the form of molecular vibration and molecular rotation. The vibration (expansion and contraction, etc.) of a molecule comprising only a few atoms has a period of the order of 10xe2x88x9213 to 10xe2x88x9214 seconds (oscillation frequency 10 to 100 THz). The rotational period is of the order of 10xe2x88x9211 to 10xe2x88x9212 seconds (rotation frequency 100 GHz to 1 THz). These periods are extremely short, and it is difficult to control these phases with existing techniques. The present invention solves this problem.
The present invention is a method of controlling rotational period and phase by means of resonance between the molecule and an external electromagnetic field. Using an alternating current scanning tunneling microscope, AC electromagnetic fields of 0 to 20 GHz can be applied to a molecule absorbed on a solid surface. Using this equipment, it is possible to lower the rotation frequency to a level at which it becomes technically possible to control. In a preferred embodiment, the aforementioned rotational resonance is ensured by attaching different functional groups, which have interactive potentials that each work attractively or repulsively with the external electromagnetic field, to terminals of the rotating element in the molecule. This method lowers the speed of rotation to a level at which it can be controlled and measured by existing techniques.
In order to read the phase information, a reference point is chosen for the rotational period of the molecule, and phase differences are read with respect to this reference point. The reference point is preferably the phase of the alternating current electromagnetic field that was first applied to the molecule so as to rotate it. Subsequently, an electromagnetic field is applied to the molecule, continuously or as a pulse, in order to shift the phase of the molecule. Thus, the phase difference is measured by observing the difference between the phase of the electromagnetic field which was first applied to the molecule and the phase of rotation of the molecule after the phase has been changed.
Herein, the term xe2x80x9cphase differencexe2x80x9d refers to the xe2x80x9crotational shiftxe2x80x9d of the molecule. If a molecule is not rotating, it does not have what is referred to herein as phase information (rotational phase information).
The parameter that is stored is the rotational phase difference of the molecule with respect to the phase of the electromagnetic field. Thus, in order to maintain this storage, it is necessary to maintain the rotation of the molecule. In order to achieve this, the storage device is scaled at the molecular scale to lower the friction and resistance of the molecule in rotation.
The method of the present invention includes the steps of rotating a molecule having a predetermined structure by applying a first alternating current electromagnetic field to the molecule, wherein the first alternating current electromagnetic field is produced by an electromagnetic field generation means that is set to a predetermined phase, controlling a rotational phase of the molecule by applying a second electromagnetic field to the rotated molecule by an information recording means, detecting a signal using a signal detection means in accordance with a rotation of the molecule having the rotational phase which has been controlled, and outputting a shift between the phase of the first alternating current electromagnetic field and a phase of the detection signal from the signal detection means as information by an information reading means.
In a preferred embodiment, the electromagnetic field generation means, the information recording means, and the signal detection means comprise a tip of a scanning tunneling microscope.
In another preferred embodiment, a plurality of functional groups are provided at a plurality of terminals of a rotating element of the molecule. The functional groups are attracted or repulsed by the external electromagnetic field.
In yet another preferred embodiment, the method further comprises the step of detecting a tunnel current in accordance with the rotation of the molecule, wherein the current signal detection means detects the tunnel current.